The spin Hamiltonian parameters g// and g^ for the interstitial V4+ in anatase are theoretically studied from the complete diagonalization (of energy matrix) method (CDM) and the perturbation theory method (PTM) which are improved in this paper. The two methods are based on the two-spin–orbit-parameter model considering the contributions from the spin–orbit (SO) coupling of central 3dn ion and ligand. The theoretical results from both methods are not only consistent with the experimental values, but also close to each other. This means that both methods can be effective in the investigations of spin Hamiltonian(SH ) parameters.
